1. Field of the Invention
The present invention relates to a nonreciprocal circuit device, particularly to a nonreciprocal circuit device such as an isolator or circulator or the like used with microwave band communication devices, and to a communication device.
2. Description of the Related Art
Generally, lumped parameter isolators employed with mobile communication devices such as cellular telephones or the like have functions for allowing signals to pass only on the sending direction, and preventing sending thereof in the reverse direction. Also, demand for reductions in size, weight, and price has increased for recent mobile communication devices, which means that reductions in size, weight, and price is also demanded for isolators.
The following structure has been proposed for such lumped parameter isolators. That is, a resin terminal case is provided on a lower yoke formed of a magnetic metal, a center electrode assembly and matching capacitors and the like are accommodated in the terminal case, and an upper yoke formed of a magnetic metal is mounted. A permanent magnet is applied to the inner side of the upper yoke, and a DC magnetic field is applied to the center electrode assembly by this permanent magnet.
Now, this isolator prevents short-circuiting between the matching capacitor and upper yoke which are in close proximity, so a proposal has bene made to apply an insulating material (e.g., an epoxy resin) on the upper yoke so as to form an insulating film. However, in this case applying insulating material without irregularities so as to form a uniform film thickness is difficult, and in the event that there are irregularities in thickness, there is concern of the matching capacitor and the upper yoke short-circuiting at this portion. Also, the applying procedure would be complicated and inefficient, which would lead to increased cost.
Accordingly, it is an object of the present invention to prevent short-circuiting between the matching capacitor and yoke in a sure manner, and provide a nonreciprocal circuit device and a communication device with high reliability and low cost.
To this end, the nonreciprocal circuit device according to the present invention comprises:
a permanent magnet; a ferrite to which a direct current magnetic field is applied by the permanent magnet, the ferrite including a plurality of center electrodes; matching capacitors electrically connected to the center electrodes; a yoke for accommodating the permanent magnet, ferrite, center electrodes, and matching capacitors; wherein insulating tape having an adhesive layer is attached to a part of the yoke in the vicinity of the matching capacitors.
At least one of the matching capacitors is preferably arranged such that the electrode face of the capacitor defines an angle in a range of 60 degrees or more to 120 degrees or less with respect to said ferrite. Also, the insulating tape preferably comprises a material with a thermal deformation temperature of 200xc2x0 C. or greater. Specifically, polyimide resin, polyamide resin, or fluororesin or the like may be used for the insulating tape, and a silicone adhesive agent or an acrylic adhesive agent may be used for the material of the adhesive layer of the insulating tape.
The above configuration prevents short-circuiting between the matching capacitor and the yoke with the insulating tape. The insulating tape has a uniform thickness, and there are no irregularities in film thickness, so short-circuiting between the matching capacitor and the yoke is reliably prevented.
Also, the communication device according to the present invention comprises a nonreciprocal circuit device with the above-described characteristics, and thus has high reliability with low manufacturing cost.